Infectious cDNA clones of picornaviruses have been produced in several laboratories following the poliovirus (PV) work of Racaniello (Science 214, 916-919). Chimeric PV's have been made in which short portions of one type of complementary cDNA from one type of picornavirus DNA has been inserted into the infectious cDNA of another type of PV (Martin, et al., EMBO Journal, 7, (1988) 2839-2847). Long segments have also been exchanged between PV types (Korhara, et al., J. Virol, 62 (1988), 2828-2835). Chimeras of PV and hepatitis A virus (HAV) have also been produced in several laboratories in which small segments of HAV cDNA representing putative antigen coding regions have been inserted into infectious cDNA of PV. However, none of these constructs have produced viruses that express HAV antigens. It is possible that the correct coding regions have not been inserted, but it is also likely that the epitopes of HAV are conformational. For instance, we have produced an "epitope library" in lambda gtll consisting of random fragments of the HAV capsid coding region. When this library was screened with neutralizing monoclonal antibodies to HAV, no clones were detected. However, when the library was screened with antibodies to synthetic oligopeptides representing regions VP1, VP2, VP3, and VP4, many positive clones were identified. These results suggest that the neutralization epitopes of HAV are non-linear. It is possible that a complete copy of one of the capsid proteins expressed as part of the PV capsid would assume the necessary three dimensional structure to represent a neutralizing epitope of HAV. In the past chimeric cDNA's with large inserts have been difficult to make requiring either the presence of convenient restriction enzyme sites or sophisticated and complicated genetic engineering. In fact, common restriction sites rarely exist in different viral species such as HAV and PV.